1. Field of the Invention
The present invention relates to an apparatus for mounting an electronic part, and more particularly, to an apparatus and a method for mounting an air-core coil.
2. Description of the Prior Art
Automatic electronic part mounting apparatuses are used to efficiently mount various types of electronic parts on a printed circuit board. The automatic electronic part mounting apparatus has a plurality of part feeding units and a pick and place unit which takes a part out of a part supplier and carries it to mount it on the printed circuit board. The following types of electronic part mounting apparatuses have been put into practical use: a Cartesian coordinates type having one pick and place unit; and a rotary table type having a plurality of pick and place heads arranged around a rotary index table. Electronic parts are supplied, for example, being in a plastic-made tape 7 having pockets 8 for holding the parts therein as shown in FIGS. 7 and 19. The width of the tape 7 and the size of the pockets 8 vary according to the size of the parts held therein. The tape 7 is conveyed at a predetermined timing at a pitch according to the distance between the pockets 8 so that the electronic parts are supplied one after another.
The commonest method employed by the pick and place units is to suck the electronic part by vacuum suction. The pick and place unit sucks an electronic part to take it out of the pocket of the tape, and carries it to mount it on a predetermined position on a printed circuit board arranged at a predetermined position. The pick and place unit provided at an upper portion of the automatic electronic part mounting apparatus includes an X-Y table movable horizontally, a head attached to the undersurface of the X-Y table so as to be movable upward and downward, and a nozzle arranged at the lower end of the head for sucking the parts. The nozzle is formed to fit the size and configuration of the parts. Several kinds of nozzles are available for the pick and place unit so that an appropriate nozzle for the part to be mounted may be selected thereamong.
The nozzle selected according to the part is moved by the movement of the X-Y table to a position above the electronic part held in the pocket of the tape. Then, the nozzle is lowered to the vicinity of the top surface of the electronic part by the downward movement of the head, and sucks the electronic part by vacuum suction to take it out of the pocket. Thereafter, the head moves upward, and the X-Y table moves to move the nozzle to a position above a predetermined position on the circuit board. Then, the head moves downward again, and when the bottom surface of the electronic part comes in contact with the circuit board, the head stops sucking the part to mount it on the predetermined position on the circuit board.
Various electronic parts such as a semiconductor chip, a capacitor and a resistor are mounted on the printed circuit board, and an air-core coil is one of such electronic parts. The air-core coil has terminals 4 horizontally protruding from both ends of coil turns 5 in the opposite directions as shown in FIGS. 17 and 18. The number of turns and the diameter of the turns vary according to the purpose, and various kinds of air-core coils have been put into practical use. When supplied for an automatic electronic part mounting apparatus, the air-core coil 3 is held in the pocket 8 of the tape 7 with its terminals 4 located at the bottom as shown in FIG. 19.
The portion of the nozzle which comes in contact with the electronic part is processed into a configuration in accordance with the configuration of the part so that the nozzle surely sucks the part without dropping it while carrying it. For example, Japanese Laid-open Utility Model Application S58-105199 discloses a nozzle of a configuration as shown in FIG. 1. This type of nozzle is suitable for sucking a cylindrical electronic part with enlarged ends. A nozzle as shown in FIG. 2 having a notch for fitting the part therein is also popular. This type of nozzle can be used for cylindrical electronic parts of various diameters which differs within a predetermined range.
However, when nozzles of these types are used for sucking air-core coils, the air-core coil 3 is sucked being inclined so that the terminals 4 may not be horizontal as shown in FIG. 2. When the air-core coil 3 is pressed against the upper surface of the circuit board under this condition, since the coil turns 5 which are fixed to the nozzle by suction cannot rotate and the terminals 4 are tend to be yielding, the lower terminal is readily deformed to be parallel to the upper surface of the circuit board. At this time, since the upper terminal 4 is not parallel to the upper surface of the circuit board, the terminals 4 of the air-core coil 3 mounted on the circuit board cannot be in close contact with the circuit board, which results in a defective electrical connection.
In many recent automatic electronic part mounting apparatuses, image recognition of the electronic part sucked by the nozzle is performed to correct the position and the angle for mounting. Defective parts are also detected in this process. Electronic parts having their terminals inclined are judged to be defective parts "with inclined leads", and such parts are thrown away. The above-mentioned air-core coil sucked being inclined may be judged to be a defective part "with inclined leads". Then, the air-core coil will be abandoned although it is not defective as a part.